Image aligning method for thermal imaging printer

ABSTRACT

An image aligning method for a thermal imaging device includes picking up a thermal imaging medium that has a first surface and a second surface on which printing operations may be performed respectively from a medium container. An edge of the medium is fed a first distance from a heating element of a thermal printhead to a printing path. An image is formed on the first surface of the medium while proceeding the medium through the printing path. The thermal printhead is rotated to face the thermal printhead toward the second surface of the medium. The edge of the medium is fed the first distance from the heating element. An image is formed on the second surface of the medium while feeding the medium through the printing path.

BACKGROUND OF THE INVENTION

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanPatent Application No. 2003-101585, filed on Dec. 31, 2003, in theKorean Intellectual Property Office, the entire disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an image aligning method for a thermalimaging printer. More particularly, the present invention relates to animage aligning method for a thermal imaging printer using a duplexthermal imaging medium.

DESCRIPTION OF THE RELATED ART

A thermal imaging printer can be divided into a printer using a mediumthat reveals a predetermined color in response to heat, and a printerusing an ink ribbon that transfers a predetermined color onto a sheet ofmedium in response to heat in order to print images on normal medium.Since the printer using the ink ribbon should include a driving devicein order to drive the ink ribbon, the structure of the printer becomescomplex and raises its price. Also, the ink ribbon should be replacedcontinuously, and, therefore, the printing cost per sheet of medium alsoincreases.

Referring to FIG. 1, ink layers 12 and 13 of predetermined colors areformed on both surfaces of a base sheet 11 of a thermal imaging medium10, that is, on a first surface and a second surface. The ink layers 12and 13 may be formed as a single layer of a mono-color ink ormulti-layers to represent two or more colors, respectively. For example,the ink layer 12 on the first surface includes two layers forrepresenting magenta (M) and cyan (C) colors, and the ink layer 13 onthe second surface is formed of a single layer for representing yellow(Y) color. It is desirable that the base sheet 11 is a transparentmaterial. U.S. Pat. No. 6,801,233 discloses an example of a thermalimaging medium 10.

In the thermal imaging printer using the thermal imaging medium 10, athermal printhead (TPH), in which heating elements are disposedperpendicularly to a direction of movement of the thermal imagingmedium, is used. To print in duplex using one TPH, printing of the firstsurface of the medium is performed, and then, the printing operation isperformed on the second surface of the medium again using the TPH. Afterprinting both surfaces of the medium, the color image is visible fromthe surface of the medium.

When the TPH is rotated in order to print the image on the secondsurface after printing the image on the first surface, the medium andthe TPH should be aligned, otherwise, the color printing operation canbe inferior.

Therefore, a need exists for a method of aligning the medium when theprinting operation of the second surface is performed after performingthe printing operation on the first surface of the medium.

SUMMARY OF THE INVENTION

The present invention provides a method of aligning printing mediums forperforming duplex printing.

According to an aspect of the present invention, a method of aligningimages for a thermal imaging device is provided (a) picking up a thermalimaging medium that has a first surface and a second surface, on whichprinting operations may be performed respectively, from a mediumcontainer, and feeding an edge of the medium a first distance from aheating element of a thermal printhead to a printing path; (b) formingan image on the first surface of the medium while moving the mediumthrough the printing path; (c) rotating the thermal printhead so thatthe thermal printhead may face the second surface of the medium; (d)feeding the edge of the medium the first distance from the heatingelement; and (e) forming an image on the second surface of the mediumwhile feeding the medium through the printing path, wherein a distancebetween an edge detection sensor that is attached at the thermalprinthead and the edge of the medium is measured to make the firstdistances in step (a) and step (d) substantially equal.

Step (a) may include picking up the medium; feeding the picked-up mediumto the printing path; detecting the edge of the medium using the edgedetection sensor; and feeding the medium a third distance when the edgeis detected using a second distance between the edge detection sensorand the thermal printhead that is stored in advance, so that the mediummay be fed the first distance from the heating element of the thermalprinthead.

According to and aspect of the present invention, the edge detectionsensor is attached on the feeding roller side of the thermal printhead,and the third distance may be a sum of the first distance and the seconddistance.

The feeding of the medium as much as the first distance by detecting theedge of the medium may include printing a test pattern on the medium byfeeding the medium the third distance from the point when the edge isdetected; detecting the test pattern using the edge detection sensor byfeeding the medium; and when the test pattern is detected, measuring afeeding distance of the medium until the test pattern is detected; andstoring the measured distance as the second distance.

Step (d) may further include feeding the medium to the printing path bydriving the feeding roller; detecting the edge of the medium using theedge detection sensor; and feeding the medium a fourth distance when theedge is detected, wherein the fourth distance is obtained by subtractingthe second distance from the first distance.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view illustrating a structure of a thermalimaging medium used in an image aligning method according to the presentinvention;

FIG. 2 is a schematic block diagram of a thermal imaging apparatus ofthe image aligning method according to the present invention;

FIG. 3 is a schematic plan view illustrating a structure of an apparatushaving the image aligning method according to the present invention;

FIG. 4 is a side elevational view illustrating the apparatus of FIG. 3;

FIG. 5 is a flow chart illustrating the image aligning method accordingto a preferred embodiment of the present invention;

FIGS. 6A through 6D are schematic views illustrating a printing processusing the image aligning method of FIG. 5;

FIG. 7 is a flow chart illustrating a method of measuring a seconddistance between a heating element of a thermal printhead (TPH) and anedge detection sensor in a case where the edge detection sensor isdisposed in front of the TPH on a backfeeding path;

FIG. 8 is a top plan view illustrating a position where a test patternis printed in FIG. 7; and

FIG. 9 is a flow chart illustrating a method of measuring a seconddistance between the heating element of the TPH and the edge detectionsensor in a case where the edge detection sensor is disposed rearwardlyof the TPH on the backfeeding path.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an image aligning method for a thermal imaging deviceaccording to exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 2 is a view illustrating an image aligning method for the thermalimaging apparatus according to exemplary embodiments of the presentinvention.

As shown in FIG. 2, the image aligning method includes at least a firstpath, a second path, and a third path, and conveys a thermal imagingmedium 10 through the paths. The first path is a medium supplying pathto supply the medium 10 to the second path. The second path is a regionwhere the medium 10 is backfed in arrow B direction to align the medium10, and fed forward in arrow F direction to print thereon. In addition,the third path is a region where the medium 10 with a printed firstsurface is located to return to the second path and the medium 10 withtwo printed surfaces is passed to discharge finally.

A medium guide 65 is disposed between the first path and the third path.The medium guide 65 guides the medium 10 to move from the first path tothe second path, and guides the medium 10 from the second path to movetoward the third path. Also, the medium guide 65 prevents the medium 10on the second path from moving toward the first path, and guides themedium 10 on the first path to move toward the second path. Thestructure and design of the medium guide 65 are generally known in theart, thus detailed descriptions for these elements are omitted.

In the second path, an image is formed by an image forming unit 50. Theimage forming process may be performed two times or more. However, inexemplary embodiments of the present invention, the image formingprocess is performed twice for a first surface and a second surface ofthe medium 10. Before forming the images on the first surface and thesecond surface of the medium 10, positions or locations of a thermalprinthead (TPH) 51 and a platen roller 55 in the image forming unit 50should be determined in advance. That is, for example, when the image isformed on the first surface of the medium 10, the TPH 51 should belocated at position C in FIG. 2, and when the image is formed on thesecond surface of the medium 10, the TPH 51 should be located atposition D. Preferably, the change of location or position of the TPH 51is made by rotating the platen roller 55 and the TPH 51 that areconnected to a rotary shaft of the platen roller 55. The change of TPH51 location is made when an interruption between the TPH 51 and themedium 10 does not occur. For example, the position of the platen roller55 and the TPH 51 may be changed before the medium 10 is supplied fromthe first path, or when the medium 10 is conveyed to the third pathduring the image forming process of the first surface.

When the medium 10, the first surface of which includes the image formedthereon, is backfed to the second path, the image forming process forthe second surface is performed by the TPH 51, the position of which ischanged. In the above process, the medium 10 moves gradually by theconveying unit 40, and moves further when the image forming on thesecond surface is completed and the medium is to be discharged throughthe medium discharging unit. The conveying unit 40 includes a feedingroller 41 that conveys the medium, and an idle roller 42 that pushes themedium entering therebetween toward the feeding roller 41.

Reference numeral 70 denotes a medium container, and reference numeral72 denotes a pickup roller to supply the medium.

The medium discharging unit 60 includes a discharging roller 61 and anidle roller 62. One roller may be disposed to perform two functions ofthe discharging roller 61 and the pickup roller 72.

FIG. 3 is a schematic plan view illustrating a structure of an apparatususing the image aligning method with the thermal imaging apparatusaccording to a preferred embodiment of the present invention. FIG. 4 isa schematic side view of the apparatus shown in FIG. 3.

Referring to FIGS. 3 and 4, the thermal imaging medium 10 enteringbetween the platen roller 55 and the TPH 51 is controlled by the feedingroller 41. An edge detection sensor 53, for example, an optical sensorto detect an edge of the medium 10 is installed at the TPH 51.

The medium 10 is conveyed in the direction indicated by arrow B, thatis, in the backfeeding direction, and in the direction indicated byarrow F direction, that is, in the printing processing direction. Anencoder disc wheel 45 is mounted on a circumference of the feedingroller 41. Slits 45 a are formed on an edge of the encoder disc wheel 45at predetermined intervals, and rotary encoder sensors 46 including alight emitting unit 46 a and a light receiving unit 46 b are mounted onboth sides of the encoder disc wheel 45. The light emitting unit 46 a ofthe rotary encoder sensor 46 emits the light at a predetermined speed,and the light receiving unit 46 b generates pulse signals whenever itreceives the light through the slit 45 a. A controller 80 counts thepulse signals to measure the conveyed distance of the medium 10 that isconveyed by the feeding roller 41, and drives the driving motor 47 tocontrol the conveyed distance of the medium 10 that is conveyed by thefeeding roller 41.

The optical sensor 53 is disposed on a lower portion or a side of theTPH 51. A plurality of heating elements 52 are disposed at apredetermined resolution under TPH 51.

The thermal imaging printer includes a rotating unit 57 that rotates theTPH 51 and the platen roller 55 through a 180° angle to print the imageon the second surface after performing the printing operation on thefirst surface of the medium 10. A vertical moving unit 59 moves the TPH51 away from the printing path or pushes the TPH 51 toward to theprinting path.

The image aligning method for the thermal imaging device will bedescribed with reference to accompanying drawings.

FIG. 5 is a flow chart describing the image aligning method for thethermal imaging printer according to the present invention. FIGS. 6Athrough 6D are schematic views illustrating the image aligning processesshown in FIG. 5.

In step 101, when a command for printing is input into the controller80, a medium 10 is picked up from the medium container 70 by the pickuproller 72 and the medium 10 proceeds to the first path.

In step 102, the medium 10 entering the first path is supplied to thefeeding roller 41 by the medium guide 65, and the feeding roller 41makes the medium 10 second path. Here, it is desirable that the TPH 51is separated from the platen roller 55 by a predetermined height. Themedium 10 entering the second path should proceed to a predeterminedlocation for performing the printing operation. Thus, the rotation ofthe rotary encoder wheel 45, which is installed on the circumference ofthe feeding roller 41, is detected by the rotary encoder sensor 46. Inaddition, when a generated pulse signal is transmitted to the controller80, the controller 80 counts the pulse signals to measure the conveyeddistance.

In step 103, the optical sensor 53, that is, the edge detection sensorinstalled on the TPH 51 detects a front edge portion of the medium 10.FIG. 6A shows the detection of an edge of the backfed medium 10 by theoptical sensor 53. Here, the TPH 51 is separated by a predeterminedheight from the medium feeding path.

In step 103, when the front edge of the medium 10 is detected, the edgedetection sensor 53 transmits an edge detection signal to the controller80.

In addition, the controller 80 moves the medium 10 in the backfeddirection as much as a first distance D1 from the heating element 52 ofthe TPH 51, as shown in FIG. 6B (step 104).

If a second distance D2, that is, a distance between the edge detectionsensor 53 and the heating element 52 of the TPH 51, is stored in thecontroller 80, the controller 80 backfeeds the medium 10 as much as athird distance D3 (first distance D1+second distance D2) to the feedingroller 41 since the edge of the medium 10 is detected. In addition, themedium 10 that is backfed to be separated the first distance D1 from theTPH 51 by the feeding roller 41 is stopped. FIG. 6B shows the state thatthe medium 10 is backfed as much as the third distance D3 from theoptical sensor 53. Here, the region of first distance D1 is the regionwhere the printing operation is performed.

Then, the TPH 51 is moved toward the medium 10, and the feeding roller51 is reversely rotated to forwardly feed the medium 10 in the directionindicated by arrow F while the image forming process for the firstsurface (the upper surface in the drawings) is performed using the TPH51 (step 105). Here, the medium 10 is conveyed toward the third path.

Then, in step 106, the edge of the medium 10, which is in the process offorward feeding, is detected by the optical sensor 53. The detection ofthe edge is performed after the image forming process for the firstsurface is completed.

When the edge of the medium 10 is detected in step 106, the controller80 proceeds the feeding roller 41 a predetermined distance further sincethe edge has been detected, and then, the controller 80 stops thefeeding of the medium 10 and rotates the image forming unit 50 toinverse the position or location of the TPH 51 so that the TPH 51 facesthe second surface of the medium 10 (step 107). FIG. 6C shows the statewhere the position of the TPH 51 is inversed. Here, the medium 10 is nottouched by the image forming unit 50 that has been rotated.

In addition, in step 108, the TPH 51 is moved toward the platen roller55 to form a gap through which the medium 10 may pass without resistancebetween the platen roller 55 and the TPH 51. After that, the medium 10is backfed to the second path to prepare the image forming process ofthe second surface by the conveying unit 40.

In step 109, the front edge of the medium 10 is detected again by theedge detection sensor 53 at the TPH 51.

When the front edge of the medium 10 is detected in step 109, the edgedetection sensor 53 transmits an edge detection signal to the controller80.

In addition, if the second distance D2 between the edge detection sensor53 and the heating element 52 of the TPH 51 is stored in the controller80, the controller backfeeds the medium 10 as much as a fourth distanceD4 (first distance D1−second distance D2) between the front edge of themedium 10 and the heating element 52 of the TPH 51, by the feedingroller 41 (step 110). Next, the medium 10 that is backfed to beseparated the first distance D1 from the TPH 51 by the feeding roller 41is stopped. FIG. 6D shows the medium 10 that is backfed as much as thefirst distance D1 from the heating element 52.

The TPH 51 is moved toward and adhered to the medium 10. The medium 10is fed forwardly by the feeding roller 41 and the image forming processfor the second surface (lower surface in the drawings) of the medium 10is performed using the TPH 51 (step 111). Here, the medium 10 is fedtoward the third path.

When the image forming process for the second surface of the medium 10is completed, the medium feeding operation by the conveying unit 40 isterminated, and the medium 10 is moved by the medium discharging unit 60to be discharged out of the printer (step 112).

FIG. 7 is a flow chart illustrating a method of measuring the seconddistance D2 between the heating element 52 of the TPH 51 and the edgedetection sensor 53 when the edge detection sensor 53 is disposed on anupstream side of the TPH 51 on the backfeeding path.

When the medium 10 is supplied to the feeding roller 41 after beingpicked up from the medium container 70, the medium 10 is backfed to thesecond path (step 201). A position of the medium 10 entering the secondpath is detected by the rotation of the rotary encoder wheel 45 that isinstalled on the circumference of the feeding roller 41 using the rotaryencoder sensor 46. Here, the generated pulse signals are transmitted tothe controller 80, and then, the controller 80 counts the pulse signalsto measure the medium conveyed distance of the medium 10.

The edge detection sensor 53 that is installed on a side of the TPH 51detects the front edge of the entering medium 10 (step 202).

In step 202, when the front edge of the medium 10 is detected, the edgedetection sensor 53 transmits the edge detection signal to thecontroller 80.

In addition, the controller 80 backfeeds the medium 10 by the feedingroller 41 as much as a predetermined distance, for example, the thirddistance D3 in FIG. 6B since the edge has been detected (step 203).

In step 204, a predetermined test pattern is printed on the medium 10.Here, it is desirable that the portion where the test pattern is printedis not the area I where the image is formed, but a tear-off area T asshown in FIG. 8. That is, since the tear-off area T that is engaged bythe feeding roller 41 at the printing start position in the printingdirection, in the direction indicated by arrow F, is removed from theimage area I after the printing operation is completed, the printing ofthe test pattern does not affect the image area I. A position of thetest pattern is detected by the edge detection sensor 53.

In step 205, the feeding roller 41 is reversely rotated to feed themedium 10 forward and the printing operation is performed. Here, in step206, the test pattern is detected.

In step 206, when the test pattern is detected, the edge detectionsensor 53 transmits a test pattern detection signal to the controller80. The controller 80 counts the pulse signals from the rotary encodersensor 46 and calculates the distance of forward feeding until the pointwhen the test pattern is detected, and stores the distance as the seconddistance D2 (step 207).

FIG. 9 is a flow chart illustrating a method of measuring the seconddistance D2 between the heating element 52 of the TPH 51 and the edgedetection sensor 53, as shown in FIG. 6D when the edge detection sensor53 is disposed at the downstream of the TPH 51 on the backfeeding path.

In step 301, the medium 10 is backfed to the second path in a state thatthe medium 10 is supplied to the feeding roller 41 after being picked upfrom the medium container 70. The position of the medium 10 that entersthe second path is detected by the rotation of the rotary encoder wheel45 installed on the circumference of the feeding roller 41 using therotary encoder sensor 46. When the generated pulse signals aretransmitted to the controller 80, the controller 80 counts the pulsesignals to measure the conveyed distance.

In addition, in step 302, the edge detection sensor installed on a sideof the TPH 51 detects the front edge of the entering medium 10.

In step 302, when the front edge of the medium 10 is detected, the edgedetection sensor 53 transmits the edge detection signal to thecontroller 80.

Then, in step 303, a predetermined test pattern is printed on the medium10.

The medium 10, on which the test pattern is printed, is backfed to thefeeding roller 41 as much as a predetermined distance, for example, thefourth distance D4 in FIG. 6D after detecting the edge (step 304).

In step 304, when the test pattern is detected (step 305), the edgedetection sensor 53 transmits the test pattern detection signal to thecontroller 80, the controller 80 counts the pulse signals from therotary encoder sensor 46 to calculate the backfeeding distance from thepoint when the test pattern is printed to the point when the testpattern is detected. The calculated distance is stored as the seconddistance D2 (step 306).

As described above, when the first surface and the second surface of thethermal imaging medium are printed using one TPH by rotating the imageforming unit, the images on the first surface and the second surface maybe aligned without regard to the error on the printing path that isgenerated when the TPH is rotated.

Also, according to the method of aligning images, the alignment may beperformed during the printing operation, and an additional time forperforming the alignment operation is not required.

The method of the present invention may be applied to a printingapparatus of general purpose, and may be applied effectively to acompact image forming device, specifically a portable printer and aphotograph printing operation requiring high definition such as adigital image printer for a digital camera.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of aligning images for a thermal imaging device, the methodcomprising: (a) picking up a thermal imaging medium that has a firstsurface and a second surface on which printing operations may beperformed respectively from a medium container, and feeding an edge ofthe medium a first distance from a heating element of a thermalprinthead to a printing path; (b) forming an image on the first surfaceof the medium while moving the medium through the printing path; (c)rotating the thermal printhead to face the thermal printhead toward thesecond surface of the medium; (d) feeding the edge of the medium thefirst distance from the heating element; (e) forming an image on thesecond surface of the medium while feeding the medium through theprinting path, and (f) measuring a distance between an edge detectionsensor that is attached at the thermal printhead and the edge of themeasured to make the first distances in step (a) and step (d)substantially equal.
 2. The method of claim 1, wherein step (a)comprises: picking up the medium; feeding the picked-up medium to theprinting path; detecting the edge of the medium using the edge detectionsensor; and feeding the medium a third distance when the edge isdetected using a second distance between the edge detection sensor andthe thermal printhead that is stored in advance to feed the medium thefirst distance from the heating element of the thermal printhead.
 3. Themethod of claim 2, further comprising attaching the edge detectionsensor on the feeding roller side of the thermal printhead, and thethird distance is a sum of the first distance and the second distance.4. The method of claim 3, wherein feeding the medium the first distanceby detecting the edge of the medium comprises: printing a test patternon the medium by feeding the medium the third distance from the pointwhen the edge is detected; detecting the test pattern using the edgedetection sensor by feeding the medium; and measuring a feeding distanceof the medium until the test pattern is detected; and storing themeasured distance as the second distance.
 5. The method of claim 3,wherein step (d) comprises: feeding the medium to the printing path bydriving the feeding roller; detecting the edge of the medium using theedge detection sensor; feeding the medium a fourth distance when theedge is detected, and obtaining the fourth distance by subtracting thesecond distance from the first distance.
 6. The method of claim 2,further comprising positioning the edge detection sensor on an oppositeside of the feeding roller, and obtaining the third distance is bysubtracting the second distance from the first distance.
 7. The methodof claim 6, wherein feeding the medium the first distance by detectingthe edge comprises: printing the test pattern on the medium when theedge is detected; feeding the medium; detecting the test pattern usingthe edge detection sensor; calculating the feeding distance of themedium from the point when the test pattern is printed until the pointwhen the test pattern is detected, and storing the distance as thesecond distance.
 8. The method of claim 6, wherein step (d) comprises:feeding the medium to the printing path by driving the feeding roller;detecting the edge of the medium using the edge detection sensor in thefeeding process; and feeding the medium a fifth distance from the pointwhen the edge is detected, wherein the fifth distance is a sum of thefirst distance and the second distance.
 9. The method of claim 1,wherein step (b) further comprises: further moving the medium apredetermined distance on the printing path after detecting the edge.10. The method of claim 1, further comprising: discharging the mediumafter completing the forming of the image on the second surface of themedium.
 11. A thermal imaging device, comprising: a printing assemblyincluding a thermal printhead and a platen roller, the printing assemblybeing rotatable; a plurality of heating elements connected to thethermal printhead and directed toward the platen roller; a sensorconnected to the thermal printhead to detect an edge of a medium; and acontroller in communication with the sensor and adapted to align themedium in response to signals received from the sensor.
 12. The thermalimaging device of claim 11, wherein when the printing assembly is in afirst position, a first distance corresponds to an aligned mediumposition; a second distance corresponds to the distance between theplurality of heating elements and the sensor; and the third distance isa sum of the first distance and the second distance, wherein the mediumis moved the third distance.
 13. The thermal imaging device of claim 12,wherein when the printing assembly is rotated about 180 degrees to asecond position, the medium is moved a fourth distance that correspondsto the difference between the first distance and the second distance.